A known seat sliding apparatus for a vehicle is disclosed in Japanese Patent Laid Open Publication No.5(1993)-262172. This seat sliding apparatus includes a pair of lower rails that are adapted to be fixed to the vehicle floor and a pair of upper rails that are adapted to be fixed to the vehicle seat. Each of the upper rails is slidably retained by one of the lower rails.
The lower rail of this known vehicle seat sliding apparatus includes a base plate portion for being fixed to the vehicle floor, a pair of side wall portions extending upwardly from each of the two lengthwise sides of the base plate portion, and a pair of engaging portions. Each of the engaging portions is formed at an end upper edge of the side wall portions and is engaged with the upper rail.
The upper rails of this seat sliding apparatus include a base plate portion for being fixed to the vehicle seat and a pair of engaging portions. Each of the engaging portions is formed at an end of the base plate portion and extends so as to cover the engaging portion of the lower rail. The engaging portions of the lower rails project from the top of the side walls of the lower rails, and form an inverted U-shape structure. The engaging portions of the upper rails are each formed in a generally U-shaped structure which engage with the engaging portions of the lower rails such that the side wall portions of the lower rails are located between the engaging portions of the upper rail. The base plate portion of an upper rail is connected to an anchor member of the seat belt.
With such a seat sliding apparatus, because the lower rails are disposed in the upper rails, the size of the width of the lower rail must be small relative to that of the upper rails. Therefore the lateral size (i.e., the width) of the base plate portion of the lower rails must be small. Consequently, the lower rails cannot be easily fixed to the vehicle floor. When the base plate portions of the lower rails are enlarged in an attempt to more easily fix the lower rails to the vehicle floor, the upper rails must also be enlarged so that, in effect, the entire seat sliding apparatus must be enlarged to achieve a larger base plate portion.
This problem is addressed in the vehicle seat sliding apparatus disclosed in Japanese Patent Laid Open Publication No. 9(1997)-164865. This seat sliding apparatus includes a pair of upper rails which each include a base plate portion, a pair of side wall portions (for each upper rail) which each extend in the downward direction from each side of the base plate portions, and a pair of engaging portions which are each formed at each of the edges of the side wall portions.
This vehicle seat sliding apparatus further includes a pair of lower rails, each provided with a base plate portion and a pair of engaging portions, with each engaging portion being formed at the side edges of the base plate portion and extending so as to cover each of the engaging portions of the upper rail so that each of the inside walls of the engaging portions of the upper rail is disposed within the respective engaging portions in each of the lower rails.
In this apparatus, when an upward force is applied to the upper rail from the seat belt, the base plate portion of the upper rail may be deformed upwardly such that the side wall portions of the lower rails and the engaging portions topple or bend inwardly. To prevent the upper rail from being disengaged from the lower rail, the thickness of the material of the upper rail must thus be enlarged which undesirably increases the cost and weight of the overall apparatus.
In light of the foregoing, a need exists for a vehicle seat sliding apparatus that is able to prevent the upper rail from being disengaged from the lower rail.
A need also exists for a vehicle seat sliding apparatus that tends to prevent the side walls of the lower rail from deforming, even when a relatively large upward force is applied through the seat belt.